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android 事件分发源码分析

news 2025/8/27 6:01:22

1）DOWN事件触发时重置标志位；

2）判断是否拦截事件（根据FLAG_DISALLOW_INTERCEPT标志和onInterceptTouchEvent返回值）；

3）遍历子View寻找能处理事件的View，通过dispatchTransformedTouchEvent询问子View；

4）将处理事件的子View保存到mFirstTouchTarget链表；

5）后续事件根据mFirstTouchTarget和拦截状态决定分发路径。当父容器拦截时，会向子View发送CANCEL事件并清空mFirstTouchTarget。整个过程实现了从父容器到子View的事件分发与拦截机制

置空标志位置

   // 在DOWN事件的时候会置空标志位置if (actionMasked == MotionEvent.ACTION_DOWN) {// 清掉旧 TouchTarget，清空mFirstTouchTargetcancelAndClearTouchTargets(ev);// 重置 FLAG_DISALLOW_INTERCEPT 等resetTouchState();}private void cancelAndClearTouchTargets(MotionEvent event) {//清空mFirstTouchTargetclearTouchTargets();}//清空mFirstTouchTargetprivate void clearTouchTargets() {ViewGroup.TouchTarget target = mFirstTouchTarget;if (target != null) {do {ViewGroup.TouchTarget next = target.next;target.recycle();target = next;} while (target != null);mFirstTouchTarget = null;}}

第一块代码，判断事件是否由父容器拦截

  //是否拦截标志final boolean intercepted;//判断是否是DOWN事件，或者是mFirstTouchTarget第一个处理事件的Viewif (actionMasked == MotionEvent.ACTION_DOWN|| mFirstTouchTarget != null) {//requestDisallowInterceptTouchEvent决定这里的属性，true这里为true，false这里为falsefinal boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;if (!disallowIntercept) {//父容器是否拦截事件intercepted = onInterceptTouchEvent(ev);ev.setAction(action); // restore action in case it was changed} else {intercepted = false;}} else {// There are no touch targets and this action is not an initial down// so this view group continues to intercept touches.intercepted = true;}

第二块代码，决定是由父容器还是子View处理事件

     ViewGroup.TouchTarget newTouchTarget = null;boolean alreadyDispatchedToNewTouchTarget = false;//判断是否是拦截事件if (!canceled && !intercepted) {//单手指DOWN，多手指ACTION_POINTER_DOWN，鼠标DOWN ACTION_HOVER_MOVEif (actionMasked == MotionEvent.ACTION_DOWN|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {//这里newTouchTarget=null，判断是否存在子Viewif (newTouchTarget == null && childrenCount != 0) {final float x =isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);final float y =isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);// Find a child that can receive the event.// Scan children from front to back.final ArrayList<View> preorderedList = buildTouchDispatchChildList();final boolean customOrder = preorderedList == null&& isChildrenDrawingOrderEnabled();final View[] children = mChildren;//开始遍历子Viewfor (int i = childrenCount - 1; i >= 0; i--) {//确定该点位落在那个Viewif (!child.canReceivePointerEvents()|| !isTransformedTouchPointInView(x, y, child, null)) {ev.setTargetAccessibilityFocus(false);continue;}newTouchTarget = getTouchTarget(child);if (newTouchTarget != null) {// Child is already receiving touch within its bounds.// Give it the new pointer in addition to the ones it is handling.newTouchTarget.pointerIdBits |= idBitsToAssign;break;}resetCancelNextUpFlag(child);//找到落点位置的View，开始询问View是否处理事件if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {// Child wants to receive touch within its bounds.mLastTouchDownTime = ev.getDownTime();if (preorderedList != null) {// childIndex points into presorted list, find original indexfor (int j = 0; j < childrenCount; j++) {if (children[childIndex] == mChildren[j]) {mLastTouchDownIndex = j;break;}}} else {mLastTouchDownIndex = childIndex;}mLastTouchDownX = ev.getX();mLastTouchDownY = ev.getY();//有View处理事件，开始修改标志位置，将mFirstTouchTarget设置为当前处理的View，newTouchTarget = mFirstTouchTargetnewTouchTarget = addTouchTarget(child, idBitsToAssign);//表示down事件已经有View处理alreadyDispatchedToNewTouchTarget = true;break;}// The accessibility focus didn't handle the event, so clear// the flag and do a normal dispatch to all children.ev.setTargetAccessibilityFocus(false);}if (preorderedList != null) preorderedList.clear();}}//标准位进行赋值，mFirstTouchTarget = target， target.next = null，mFirstTouchTarget.next = nullprivate ViewGroup.TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {final ViewGroup.TouchTarget target = ViewGroup.TouchTarget.obtain(child, pointerIdBits);//这里mFirstTouchTarget在DOWN的时候置空了，这里为空target.next = mFirstTouchTarget;//mFirstTouchTarget赋值为当前处理事件的ViewmFirstTouchTarget = target;return target;}}dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {// Perform any necessary transformations and dispatch.if (child == null) {handled = super.dispatchTouchEvent(transformedEvent);} else {//询问子View是否处理事件final float offsetX = mScrollX - child.mLeft;final float offsetY = mScrollY - child.mTop;transformedEvent.offsetLocation(offsetX, offsetY);if (! child.hasIdentityMatrix()) {transformedEvent.transform(child.getInverseMatrix());}handled = child.dispatchTouchEvent(transformedEvent);}}

第三块代码，对其他事件继续处理

 // Check for cancelation.final boolean canceled = resetCancelNextUpFlag(this)|| actionMasked == MotionEvent.ACTION_CANCEL;//没有子View处理事件，将事件交个父容器，询问父容器是否需要处理事件if (mFirstTouchTarget == null) {//注释1：canceled = falsehandled = dispatchTransformedTouchEvent(ev, canceled, null,ViewGroup.TouchTarget.ALL_POINTER_IDS);} else {ViewGroup.TouchTarget predecessor = null;ViewGroup.TouchTarget target = mFirstTouchTarget;//mFirstTouchTarget = target， target.next = null，mFirstTouchTarget.next = null//这里不为空，执行该方法while (target != null) {//next 未空，下一次将不执行final ViewGroup.TouchTarget next = target.next;//DOWN alreadyDispatchedToNewTouchTarget = true 有View处理事件 alreadyDispatchedToNewTouchTarget = true，newTouchTarget = target = mFirstTouchTargetif (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {handled = true;} else {//DOWN事件没有处理获取其他事件 alreadyDispatchedToNewTouchTarget = falsefinal boolean cancelChild = resetCancelNextUpFlag(target.child)|| intercepted;//注释2：对已经处理的事件进行分发if (dispatchTransformedTouchEvent(ev, cancelChild,target.child, target.pointerIdBits)) {handled = true;}//当MOVE的时候，父容器拦截事件，将事件置为CANCEL事件后，将mFirstTouchTarget置空if (cancelChild) {if (predecessor == null) {mFirstTouchTarget = next;} else {predecessor.next = next;}target.recycle();target = next;continue;}}predecessor = target;target = next;}}// Update list of touch targets for pointer up or cancel, if needed.if (canceled|| actionMasked == MotionEvent.ACTION_UP|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {resetTouchState();} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {final int actionIndex = ev.getActionIndex();final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);removePointersFromTouchTargets(idBitsToRemove);}//注释1：//canceled = falsehandled = dispatchTransformedTouchEvent(ev, canceled, null,ViewGroup.TouchTarget.ALL_POINTER_IDS);private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {//child = null，询问父容器是否处理事件if (child == null) {handled = super.dispatchTouchEvent(transformedEvent);} else {final float offsetX = mScrollX - child.mLeft;final float offsetY = mScrollY - child.mTop;transformedEvent.offsetLocation(offsetX, offsetY);if (! child.hasIdentityMatrix()) {transformedEvent.transform(child.getInverseMatrix());}handled = child.dispatchTouchEvent(transformedEvent);}}//注释2：final boolean cancelChild = resetCancelNextUpFlag(target.child)|| intercepted;dispatchTransformedTouchEvent(ev, cancelChild,target.child, target.pointerIdBits)cancelChild =false;private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {if (child == null) {handled = super.dispatchTouchEvent(transformedEvent);} else {//询问子View 是否处理事件final float offsetX = mScrollX - child.mLeft;final float offsetY = mScrollY - child.mTop;transformedEvent.offsetLocation(offsetX, offsetY);if (! child.hasIdentityMatrix()) {transformedEvent.transform(child.getInverseMatrix());}handled = child.dispatchTouchEvent(transformedEvent);}}cancelChild = true;private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {//父类View拦截了事件，将事件改成cancel下发给Viewif (cancel || oldAction == MotionEvent.ACTION_CANCEL) {event.setAction(MotionEvent.ACTION_CANCEL);if (child == null) {handled = super.dispatchTouchEvent(event);} else {handled = child.dispatchTouchEvent(event);}event.setAction(oldAction);return handled;}}

事件分发场景1

DOWN事件，

条件1：父容器onInterceptTouchEvent返回false，

条件2：子View dispatchTouchEvent返回false，

条件3：父容器onTouch返回false，

事件分发2

DOWN事件，

条件1：父容器onInterceptTouchEvent返回false，

条件2：子View dispatchTouchEvent返回true，

条件3：父容器onTouch返回false，

事件分发3

DOWN事件，

条件1：父容器onInterceptTouchEvent返回false，

条件2：子View dispatchTouchEvent返回false，

条件3：父容器onTouch返回true，

事件分发4

DOWN事件，

条件1：父容器onInterceptTouchEvent返回false，

条件2：子View dispatchTouchEvent返回true，

条件3：父容器onTouch返回true，

同事件分发2，会首先响应子View的事件处理，响应后不再响应父容器的事件响应

事件分发5

如果DOWN事件是父容器拦截了，那么子View将不会再收到事件

DOWN事件，

条件1：父容器onInterceptTouchEvent返回true，

条件2：子View dispatchTouchEvent返回true或者false，

条件3：父容器onTouch返回true或者false，

事件分发6

条件1：父容器onInterceptTouchEvent返回false，

条件2：子View requestDisallowInterceptTouchEvent设置成true

条件3：子View dispatchTouchEvent返回true

条件4：父容器onTouch返回true或者false，

MOVE事件1，

条件1：父容器onInterceptTouchEvent返回true，

条件2：子View requestDisallowInterceptTouchEvent设置成false

条件3：子View dispatchTouchEvent返回true

条件4：父容器onTouch返回true，

MOVE事件2，

条件1：父容器onInterceptTouchEvent返回true，

条件2：requestDisallowInterceptTouchEvent设置成false

条件3：子View dispatchTouchEvent返回true

条件4：父容器onTouch返回true，

MOVE事件3，

条件1：父容器onInterceptTouchEvent返回true，

条件2：requestDisallowInterceptTouchEvent设置成false

条件3：子View dispatchTouchEvent返回true

条件4：父容器onTouch返回true，

子View只要在DOWN事件返回true就可以接收其他所有事件

在DOWN事件返回true的时候，会把响应的View保存到派发链表mFirstTouchTarget中，接下来的事件，只要父类不拦截，都会派发事件给当前mFirstTouchTarget保存的View，如果父容器有拦截，就会传递CANCEL事件给mFirstTouchTarget保存的View，并且把mFirstTouchTarget置空，以后的所有事件都会传给父容器

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